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Saturday, February 1, 2014

A DIY Car USB Charger: Autobattrion

Salam'alaikum everyone,

I was walking around in a shopping mall (I don't like those glitzy shopping malls at all for the record, they're noisy and our country is mushrooming with 'em. What, like you don't have enough things to buy already? Okay I'll quit before it gets off-tangent, but this article sums up quite a bit about my opinion on them. Haha.) And you know what? A simple USB car charger costs RM30! I know places where they sell it for RM5 apiece, but the point is, I prefer not buying them for the quality they give. And I'll certainly shan't fish out three red notes to pay for such a kiddie item.

Anyway. The interwebs got lots of projects like these, like:
-Instructables: A good-ish instructable, with lots of feedback. I'd have to say the comments helped a lot.
-Jason Jalopnik: A project with really nice pictures, and easy for electronics beginners.

Why build my own? Well, I had stuff lying around (my sister's old Nokia 3310 battery charger, kaput, I just need to build on what's inside) and I think it is much more... monumental, building things which you use rather than buying them. I think the reason people throw Scandinavian furniture away every other day is because it is too easy to acquire. Well.. *snap* to the apartment guys.

How does it work? For the layman, what you're getting from your car where you plug in your cigarette lighter is basically the battery power which powers up a resistive element in the lighter. So electrical energy is converted into heat, and voila. Be careful with car batteries, they potentially can shock anybody if mishandled. If you're not sure how to do it, then ask someone who knows them. This is how I'd visualize it:

Figure 1: What actually that hole in your car is all about.

Now we proceed to the small stuff. I got a UA7805, which is a sample from Texas Instruments, so it's free. (Thank you TI's Thief River Falls guys!) It will regulate the voltage from the car socket output's 12V to 5V. The rest is pretty basic; indeed that's all you need. But I wouldn't mind adding some small stuff since I got them anyway.

Next, you'd need a USB female socket. Duh. I'd like to note that since most of us use smartphones, and the adapters for charging are most likely micro-b type (Refer here for more detail). However, since most of us have the [Type-A]-to-[Type-whatever] adapters, it would be more practical for us to have a more universal socket, like Type A.

Figure 2: USB socket

Notice the keyboard buttons? I'm using it as a housing for the socket. I suppose the decline on using PCs nowadays has greatly contributed to unwanted keyboards, and I'd have to say they are super useful to make a lot of things. You'll just need to use a standard cutting knife to cut the shape so that the socket can fit snugly between the pieces. You'll see it later.

The next step is to assemble everything according to the schematic. I'm just posting the schematic for fun using Paint guys, so don't bash me if it lacks the supreme Altium-ish look.

Figure 3: Circuit for the charger, which is just really a simple voltage regulation schematic with more color on it. That's all.

A bit of elaboration needed here. Ahem. The data terminals 2 & 3 (D- and D+) of the USB socket need to be shorted for it to act as a charger. Also, I added a Schottky Diode in series with the 5V output. This will thwart the reverse power leak to the circuitry from the phone's battery. I experienced that when I plugged in my GPS device to a similar charger. It turned flat within minutes! So, something to learn here.

Here's a picture of my assembled Autobattrion (fancy name just for fun, no need to take it seriously guys):

Figure 4: Look at the perfboard, and you'd know how DIY-ish this looks.

I tested the charging by hooking up the charger to a power supply in home:

Figure 6: Clamped both keyboard button to encase the USB socket, a splash of Epoxy Glue, and a dash of black paint.

The charging in my own car went well. Alhamdulillah.

Figure 7: Charging.....

So in conclusion, I built this charger for practically zero bucks within two man-hours. I call this AutoBattrion, so that I don't have to say "I built a DIY-USB-Car-Charger". Instead I'll just say, "Hey guys, AutoBattrion." Hehe.